Fast Field Cycling NMR Relaxometry Research Articles

Conformational Redistribution of Honey Components following Different Storage Conditions

The present study aims at the investigation of the changes in water distribution among the organic components of selected honey samples following honey storage at different temperatures. Results, achieved by application of fast field cycling NMR relaxometry, revealed that the organic constituents were homogeneously distributed within the whole samples stored at room temperature. Conversely, after four months of refrigeration at 4°C, the organic systems were included in persistent clusters, as a consequence of the water release due to the larger stability of the intramolecular interactions over the intermolecular ones. The new conformational arrangements of the honey constituents entailed enhancement of honey moisture content. For this reason, it can be suggested that honey refrigeration prior to storage at room temperature may be detrimental for its long-term storage. In fact, higher risk of fermentation may occur once the sample is warmed after the first refrigeration step.

New applications and perspectives of fast field cycling NMR relaxometry.

The field cycling NMR relaxometry method (also known as fast field cycling (FFC) when instruments employing fast electrical switching of the magnetic field are used) allows determination of the spin-lattice relaxation time (T1 ) continuously over five decades of Larmor frequency. The method can be exploited to observe the T1 frequency dependence of protons, as well as any other NMR-sensitive nuclei, such as (2) H, (13) C, (31) P, and (19) F in a wide range of substances and materials. The information obtained is directly correlated with the physical/chemical properties of the compound and can be represented as a 'nuclear magnetic resonance dispersion' curve. We present some recent academic and industrial applications showing the relevance of exploiting FFC NMR relaxometry in complex materials to study the molecular dynamics or, simply, for fingerprinting or quality control purposes. The basic nuclear magnetic resonance dispersion features are outlined in representative examples of magnetic resonance imaging (MRI) contrast agents, porous media, proteins, and food stuffs. We will focus on the new directions and perspectives for the FFC technique. For instance, the introduction of the latest Wide Bore FFC NMR relaxometers allows probing, for the first time, of the dynamics of confined surface water contained in the macro-pores of carbonate rock cores. We also evidence the use of the latest field cycling technology with a new cryogen-free variable-field electromagnet, which enhances the range of available frequencies in the 2D T1 -T2 correlation spectrum for separating oil and water in crude oil. Copyright © 2015 John Wiley & Sons, Ltd.

A Comparison of Magnetometry and Relaxometry Measures of Magnetic Nanoparticles Deposited in Biological Samples

The Alternating Gradient Field Magnetometer (AGFM) is an instrument whose high sensitivity (10-8 emu) allows the detection of small amounts of magnetic nanoparticles (MNPs) with high accuracy. Over the last few years, different magnetic techniques have been used for in vitro measurements of magnetic nanostructures inside biological tissues. However, in vivo studies about their distribution within the body are very scarce because their dispersion, after being delivered, reduces their magnetic signal and hinders detection. In this paper we compare the longitudinal relaxation time (T1) and magnetization measurements in mice's biological tissues for the tracking of MNPs after of an injection of iron oxide nanoparticles. Furthermore, we have correlated the AGFM data with Fast Field Cycling NMR Relaxometry (FFCNMR Relaxometry) measurements with histological analysis. The results have demonstrated that these techniques are useful for detecting minute amounts of MNPs in excised organs after in-vivo comparable to other more conventional techniques for the measurement of MNPs biodistribution and clearance. Details about the preparation of the in vivo samples, measurement protocol and statistical data processing are given.

Water dynamics in different biochar fractions.

Biochar is a carbonaceous porous material deliberately applied to soil to improve its fertility. The mechanisms through which biochar acts on fertility are still poorly understood. The effect of biochar texture size on water dynamics was investigated here in order to provide information to address future research on nutrient mobility towards plant roots as biochar is applied as soil amendment. A poplar biochar has been stainless steel fractionated in three different textured fractions (1.0-2.0 mm, 0.3-1.0 mm and <0.3 mm, respectively). Water-saturated fractions were analyzed by fast field cycling (FFC) NMR relaxometry. Results proved that 3D exchange between bound and bulk water predominantly occurred in the coarsest fraction. However, as porosity decreased, water motion was mainly associated to a restricted 2D diffusion among the surface-site pores and the bulk-site ones. The X-ray μ-CT imaging analyses on the dry fractions revealed the lowest surface/volume ratio for the coarsest fraction, thereby corroborating the 3D water exchange mechanism hypothesized by FFC NMR relaxometry. However, multi-micrometer porosity was evidenced in all the samples. The latter finding suggested that the 3D exchange mechanism cannot even be neglected in the finest fraction as previously excluded only on the basis of NMR relaxometry results. X-ray μ-CT imaging showed heterogeneous distribution of inorganic materials inside all the fractions. The mineral components may contribute to the water relaxation mechanisms by FFC NMR relaxometry. Further studies are needed to understand the role of the inorganic particles on water dynamics.

Dynamics of Water in Hierarchical Mesoporous H-ZSM-5 by Fast Field-Cycling NMR Relaxometry

The dynamics of water molecules adsorbed in hierarchical mesoporous H-ZSM-5 was investigated by fast field-cycling NMR relaxometry. Three distinct sites in H-ZSM-5 that can host water molecules, designated a, b, and c, have been identified; no significant exchange of water molecules among these sites was observed. Investigations into the relative populations of molecules confined at sites c (Pc) and b (Pb) revealed that the population ratio (Pc/Pb) does not change significantly over the temperature and water-content ranges investigated. Furthermore, the motion of water at site b is very slow and shows almost no dependence on temperature. While H-ZSM-5 has pores of two different sizes (mesopores and micropores), the low population and observed slow motion of water at site b indicates a strong interaction between water molecules and the zeolite materials, which is possible only when water is adsorbed on the surface. The temperature of the phase transition of water provides insight into the properties of water adsorption. The transition temperature of water confined at site a varies with water content in the sample, indicating that it is located in a larger space; thus, site a represents mesopores. The transition temperature of water and the population of water molecules at site c are independent of water content, indicating that this site has been saturated; therefore, site c is the micropore, which is saturated because of capillary condensation.

The Effect of Curing Temperature on Early Hydration of Gray Cement Via Fast Field Cycling-NMR Relaxometry

In the present work, we use fast field cycling (FFC) nuclear magnetic resonance relaxometry to evaluate the influence introduced by the curing temperature on the hydration process of gray cement. The main advantage of FFC relaxometry as compared with other relaxation studies performed at a specific frequency is that it is sensitive to a wider range of molecular motions and better separates the surface and bulk contributions from the global measured relaxation rate. In the case of cement hydration, the relaxation process is dominated by the interaction of water protons with the paramagnetic centers located on the surface of cement grains. This allows us in the frame of a two-phase exchange model to monitor the temperature dependence of the transverse diffusional correlation time at the surface of cement grains. An increase of the surface diffusion coefficient of water molecules with the temperature was revealed. Another outcome is that the surface-to-volume ratio of capillary pores continuously increases during the early hydration and this process is strongly enhanced by rising the temperature.

Mechanisms of water interaction with pore systems of hydrochar and pyrochar from poplar forestry waste.

The aim of this study was to understand the water-surface interactions of two chars obtained by gasification (pyrochar) and hydrothermal carbonization (hydrochar) of a poplar biomass. The two samples revealed different chemical compositions as evidenced by solid state (13)C NMR spectroscopy. In fact, hydrochar resulted in a lignin-like material still containing oxygenated functionalities. Pyrochar was a polyaromatic system in which no heteronuclei were detected. After saturation with water, hydrochar and pyrochar were analyzed by fast field cycling (FFC) NMR relaxometry. Results showed that water movement in hydrochar was mainly confined in very small pores. Conversely, water movement in pyrochar led to the conclusion that a larger number of transitional and very large pores were present. These results were confirmed by porosity evaluation derived from gas adsorption. Variable-temperature FFC NMR experiments confirmed a slow-motion regime due to a preferential diffusion of water on the solid surface. Conversely, the higher number of large pores in pyrochar allowed slow movement only up to 50 °C. As the temperature was raised to 80 °C, water interactions with the pore surface became weaker, thereby allowing a three-dimensional water exchange with the bulk liquid. This paper has shown that pore size distribution was more important than chemical composition in affecting water movement in two chemically different charred systems.

The Effect of Cholesterol on Membrane Dynamics on Different Timescales in Lipid Bilayers from Fast Field-Cycling NMR Relaxometry Studies of Unilamellar Vesicles

The general applicability of fast field-cycling nuclear magnetic resonance relaxometry in the study of dynamics in lipid bilayers is demonstrated through analysis of binary unilamellar liposomes composed of 1,2-dioleoyl-sn-glycero-3-posphocholine (DOPC) and cholesterol. We extend an evidence-based method to simulating the NMR relaxation response, previously validated for single-component membranes, to evaluate the effect of the sterol molecule on local ordering and dynamics over multiple timescales. The relaxometric results are found to be most consistent with the partitioning of the lipid molecules into affected and unaffected portions, rather than a single averaged phase. Our analysis suggests that up to 25 mol%, each cholesterol molecule orders three DOPC molecules, providing experimental backup to the findings of many molecular dynamics studies. A methodology is established for studying dynamics on multiple timescales in unilamellar membranes of more complex compositions.

Translational diffusion at the surface of porous media with magnetic impurities via Fast Field Cycling NMR relaxometry

Translational diffusion at the surface of porous media with magnetic impurities via Fast Field Cycling NMR relaxometry

Effects of cholesterol on membrane molecular dynamics studied by fast field cycling NMR relaxometry

Biological membranes are complex structures composed of various lipids and proteins. Different membrane compositions affect viscoelastic and hydrodynamic properties of membranes, which are critical to their functions. Lipid bilayer vesicles inserted by cholesterol not only enhance membrane surface motional behavior but also strengthen vesicle stability. Cholesterol-rich vesicles are similar to cell membranes in structure and composition. Therefore, cholesterol-rich vesicles can represent a typical model for studying membrane dynamics and functions. In this study, nuclear magnetic relaxation dispersion was used to investigate the detailed molecular dynamics of membrane differences between vesicles and cholesterol vesicles in the temperature range of 278-298 K. Vesicles of two different sizes were prepared. The effect of cholesterol mainly affected the order fluctuation of membranes and the diffusional motion of lipid molecules. In addition, phase variations were also observed in liposomes that contained cholesterol from analyses of the distances between lipid molecules.

Molecular dynamics in a blue phase liquid crystal: a 1H fast field-cycling NMR relaxometry study

Liquid crystals exhibiting Blue Phases (BPs) have been the focus of academic and commercial research interest in the last few years due to their highly interesting properties in the fields of optics and photonics. In order to better understand the properties of the BPs, it is important to study molecular dynamics in these phases, including molecular rotations/reorientations, diffusion, and collective motions. Here, we present the first study of molecular dynamics in a BP system by means of 1H fast field-cycling relaxometry. The investigated sample, called 10BBL, was a lactate derivative, containing two chiral centers, exhibiting BP, TGBA*, TGBC*, and SmC* phases stable in rather large temperature ranges. Molecular dynamics was investigated by analyzing the temperature- and frequency-dependencies of spin-lattice relaxation. We compare the dynamics in the TGB phases with the one in the BP and with the TGB phases investigated in previous studies.

Nature of water‐biochar interface interactions

AbstractA poplar biochar obtained by an industrial gasification process was saturated with water and analyzed using fast field cycling (FFC) NMR relaxometry in a temperature range between 299 and 353 K. Results revealed that the longitudinal relaxation rate increased with the increment of the temperature. This behavior was consistent with that already observed for paramagnetic inorganic porous media for which two different relaxation mechanisms can be accounted for: outer‐ and inner‐sphere mechanisms. The former is due to water diffusing from the closest approach distance to infinity, whereas the second is due to water interacting by nonconventional H‐bonds to the porous surface of the solid material. In particular, the inner‐sphere relaxation appeared to be predominant in the water‐saturated biochar used in the present study. This study represents a fundamental first step for the full comprehension of the role played by biochar in the draining properties of biochar‐amended soils.

Collective and molecular motions of fluorinated liquid crystals by means of 19F Fast Field-Cycling NMR relaxometry

19F Fast Field-Cycling (FFC) NMR relaxometry was applied for the first time for the investigation of the dynamics of a liquid crystal. Longitudinal 19F relaxation rates were measured at different temperatures in the nematic phase of 4DBF2 in the frequency range between about 9.5kHz and 33MHz. The observed relaxation dispersions could be well reproduced using a simple model in which contributions due to order director fluctuations and molecular rotational diffusion motions were considered. The obtained results indicate 19F FFC NMR relaxometry as a valuable method for the investigation of molecular and collective motions of fluorinated liquid crystals.

Fast field cycling NMR relaxometry characterization of biochars obtained from an industrial thermochemical process

Purpose Biochar has unique properties which make it a powerful tool to increase soil fertility and to contribute to the decrease of the amount of atmospheric carbon dioxide through the mechanisms of C sequestration in soils. Chemical and physical biochar characteristics depend upon the technique used for its production and the biomass nature. For this reason, biochar characterization is very important in order to address its use either for agricultural or environmental purposes.

Measurement of fibrin concentration by fast field‐cycling NMR

The relaxation of (1)H nuclei due to their interaction with quadrupolar (14)N nuclei in gel structures is measured using fast field-cycling NMR. This phenomenon called quadrupolar dips has been reported in different (1)H-(14)N bond-rich species. In this study, we have studied quadrupolar dips in fibrin, an insoluble protein that is the core matrix of thrombi. Fibrin was formed by the addition of thrombin to fibrinogen in 0.2% agarose gel. T(1)-dispersion curves were measured using fast field-cycling NMR relaxometry, over the field range of 1.5-3.5 MHz (proton Larmor frequency), and were analyzed using a curve-fitting algorithm. A linear increase of signal amplitude with increasing fibrin concentration was observed. This agrees with the current theory that predicts a linear relationship of signal amplitude with the concentration of contributing (14)N spins in the sample. Interestingly, fibrin formation gave rise to the signal, regardless of crosslinking induced by the transglutaminase factor XIIIa. To investigate the effect of proteins that might be trapped in the thrombi in vivo, the plasma protein albumin was added to the fibrin gel, and an increase in the quadrupolar signal amplitude was observed. This study can potentially be useful for thrombi classification by fast field-cycling MRI techniques.

Interaction of chlorobenzene with gelator in methyl-4,6- O-( p-nitrobenzylidene)-α- d-glucopyranoside gel probed by proton fast field cycling NMR relaxometry

The solvent–gelator interactions in the gel composed of the low molecular mass gelator methyl-4,6- O-benzylidene- α- d-glucopyranoside with chlorobenzene is the subject of the studies. The interaction causes a significant slowing down of the motion of chlorobenzene molecules at the gelator surfaces when compared to bulk chlorobenzene. The motion manifests itself through the low frequency dispersion of the proton spin-lattice relaxation time of chlorobenzene in gel observed below 10 5 Hz. The relaxation time was measured with the Fast Field Cycling relaxometry method in the function of magnetic field strength and temperature. The data were interpreted in terms of two-fraction fast-exchange model.

Applicability of solid state fast field cycling NMR relaxometry in understanding relaxation properties of leaves and leaf-litters

Inversion recovery high field solid state (SS) 1H NMR spectroscopy and fast field cycling (FFC) NMR relaxometry have been applied on dried leaves and leaf-litters from a reafforestated area in central Sicily (Italy) in order to evaluate relaxation properties in both slow ( 1 ≪ ω 0 2 τ C 2 ) and fast ( 1 ≫ ω 0 2 τ C 2 ) motion regimes. Namely, SS 1H NMR spectroscopy (i.e. slow motion regime conditions) revealed that two relaxation components (a fast and a slow one) can be identified in all the leaves and leaf-litter samples. The fast component was assigned to small sized plant metabolites, whereas the slow one was attributed to slowly tumbling macropolymeric molecules. FFC NMR relaxometry (i.e. fast motion regime conditions) indicated that intra- and inter-segmental motional contributions to plant relaxation occur, depending on the nature of the plant sample under investigation. The present study represents the first example of a combination of high and low resolution NMR techniques for the understanding of the dynamics properties of environmentally relevant soft matter such as leaves and leaf-litters. These materials are considered among the main contributors for the synthesis of natural organic matter. For this reason, a comprehension of their basic molecular dynamics properties is a crucial point to evaluate their effect on, e.g., carbon cycle, fate of organic and inorganic pollutants, and microbial biomass grow.

Temperature and Size-Dependence of Membrane Molecular Dynamics in Unilamellar Vesicles by Fast Field-Cycling NMR Relaxometry

New methods to study dynamics in lipid bilayers are of interest particularly where they may bridge the gap between conventional experimental techniques and molecular dynamics simulations. Fast field cycling nuclear magnetic resonance relaxometry can provide valuable information as it is sensitive to dynamic processes that occur over a broad time scale. By analysis of data recorded for large unilamellar liposomes composed of 1,2-dimyristoyl-sn-glycero-3-posphocholine (DMPC) or 1,2-dioleoyl-sn-glycero-3-posphocholine (DOPC) at different temperatures and sizes, we validate an evidence-based approach to studying dynamics by relaxometry. Specifically, the number and form of the spectral density contributions from a range of dynamic processes are determined. This success of the approach strongly suggests its general applicability for the study of dynamics in membranes of more complex composition and for parameterizing molecular dynamics simulations.

Dynamics of hyaluronan aqueous solutions as assessed by fast field cycling NMR relaxometry

Fast field cycling (FFC) NMR relaxometry has been used to study the conformational properties of aqueous solutions of hyaluronan (HYA) at three concentrations in the range 10 to 25 mg mL(-1). Results revealed that, irrespective of the solution concentration, three different hydration layers surround hyaluronan. The inner layer consists of water molecules strongly retained in the proximity of the HYA surface. Because of their strong interactions with HYA, water molecules in this inner hydration layer are subject to very slow dynamics and have the largest correlation times. The other two hydration layers are made of water molecules which are located progressively further from the HYA surface. As a result, decreasing correlation times caused by faster molecular motion were measured. The NMRD profiles obtained by FFC-NMR relaxometry also showed peaks attributable to (1)H-(14)N quadrupole interactions. Changes in intensity and position of the quadrupolar peaks in the NMRD profiles suggested that with increasing concentration the amido group is progressively involved in the formation of weak and transient intramolecular water bridging adjacent hyaluronan chains. In this work, FFC-NMR was used for the first time to obtain deeper insight into HYA-water interactions and proved itself a powerful and promising tool in hyaluronan chemistry.

Field-Cycling NMR Relaxometry Study of Dynamic Processes in Conducting Polyaniline

Fast-field cycling NMR relaxometry been applied to investigate dynamic processes in the conducting polymer, polyaniline. For a group of samples with different concentrations of the dopant trifluoromethanesulfonic acid, the 1H spin−lattice relaxation rates exhibit power law dependence on the Larmor frequency. The powers obtained are found to increase above a percolation threshold in dopant concentration and to show similar concentration and temperature dependence as is observed for the macroscopic polymer conductivity. These observations are discussed in terms of the accepted models for both the fast polaron dynamics and the slower, low-frequency, polymer dynamics.